Over the last decades, many advances have been made in the area of microvascular surgery, particularly in the area of free flap tissue surgery. Free flaps are regularly used in plastic and reconstructive surgery, for example in breast reconstruction. In free flap surgery, tissue and/or muscle is removed from one part of the body, along with an associated artery and vein, and is reattached to another part of the body. The artery and vein of the transferred tissue and/or muscle are then anastomosed (that is, connected) to a native artery and vein in order to achieve blood circulation in the transferred tissue and/or muscle.
The anastomosis of the free flap tissue to the native tissue is typically done using microvascular techniques, including under microscopic visualization. In previous years, several surgical instruments and techniques have been developed to aid in anastomosis. One known system for creating an anastomosis is the Ventrica MVP™ System. This system includes two pairs of elliptical magnets and a delivery device. One pair of magnets is deployed to form the anastomotic port within the graft vessel. The other pair is deployed to form an identical anastomotic port within a target vessel. The graft vessel port is placed onto the target vessel to form the anastomosis.
Another known system is the JOMED SOLEM GraftConnector, a system consisting of a connector, a handle and a combined delivery and expansion activation unit. The connector is a T-shaped connector with a self-expanding stent inside the main body. The delivery handle has two L-shape holders and a center pin. The L-shaped holder facilitates insertion of the connector into a coronary artery. Once in place, release of the holder and expansion of the connector inside the artery is activated by pulling out the central needle and its cap. The self-expanding stent anchors the connector in the coronary artery without the need to suture.
A yet another known system is an anastomosis coupler, described in Applicant's own U.S. Pat. Nos. 4,607,637; 4,624,257; 4,917,090; and 4,917,091, the disclosures of which are incorporated herein by reference. This anastomotic coupler is a surgical instrument that allows a surgeon to more easily and effectively join together two blood vessel ends. A coupler of the type described is in commercial use under the tradename Microvascular Anastomotic Coupler System. It can be seen from the product literature that the coupler involves the use of two fastener portions, in the shape of rings, upon which are secured respective sections of the vessel to be attached. Each fastener portion is also provided with a series of pins, and corresponding holes for receiving those pins, in order to close and connect the portions, and in turn the vessel, together.
While free flap surgeries have a history of success, highly undesirable consequences of a flap failure still remain a possibility. One of the main causes of flap failure is a lack of blood being supplied to the flap tissue. Things that commonly disturb circulation in a flap include vascular occlusion, hemorrhage, or infection. When not enough blood is supplied to the flap tissue, tissue necrosis results. However, if it can be recognized early enough that the flap is not receiving adequate circulation, it may be saved, or salvaged. The window of time for salvaging the flap after a lack of blood flow is recognized is very small. It is therefore critical that any lack of blood flow in a transferred flap be quickly recognized.
Handheld Doppler probes are available and used by surgeons to assess vascular flow prior to or during such surgical procedures. See, for instance, the intraoperative doppler probes produced by company such as Vascular Technology, Inc. Such probes are typically permanently positioned on the distal tip of a pen-like device, rather than themselves be placed or left within the body.
Certain post-operative monitoring techniques are also used for assessing blood flow in a free flap tissue. One technique involves the use of a device such as the Cook-Swartz Doppler Flow Probe and Monitor System (see Instructions for Use by COOK Vascular™ Incorporated). This product is described as being useful for assessing vascular patency. An implantable 20 MHz ultrasonic probe properly aligned in a suturable cuff, which provides direct vessel monitoring of microvascular anastomoses at a specific site along a designated vessel. The absence of the monitor's audible signal alerts the medical staff that a potential problem with perfusion may exist, thus providing the opportunity for early intervention.
The product literature goes to describe it as a 1 mm piezoelectric crystal that is placed directly on the vessel to provide a means of monitoring flow with specificity of vessel origin (in-situ 3-7 days). When vessel monitoring is completed, the probe may be removed by applying minimal traction, leaving only the cuff in-situ. A troubleshooting protocol including cable and channel verifiers, along with an internal self test circuit in monitor, is said to allow for patient assessment. The cuff itself (which is said to be patented) secures the crystal to the vessel in proper alignment. Retention tabs are provided for strain relief, in an attempt to reduce the chance of accidental crystal dislodgement. Battery operation allows portability for monitoring at any location. Unfortunately, devices such as that described above continue to suffer from various drawbacks, including in particular the fact that the probe itself is in an approximate position that is less than optimal (approximately 90 degrees to the flow of blood). Moreover, the position of both the cuff, and in turn the probe itself, is unpredictable and itself subject to change, e.g., as the cuff moves along and/or around the vessel, or even when the patient himself changes positions.
See also U.S. Pat. No. 5,588,436 to Narayanan et al., which provides what appears to be an intravascular application of Doppler monitoring. The '436 patent describes the manner in which the use of Doppler involves monitoring blood flow following vessel anastomosis as a part of organ transplant, reconstructive surgery, and other procedures where small vessels must be reattached and can frequently close off following surgery. Instruments developed for this purpose have involved securing the Doppler transducer head to the vessel, such as with a cuff, then closing the incision with the conductor wires exiting the patient where they are attached to an appropriate ultrasound frequency generator, back-scattering sensor, and control computer.
The '436 patent goes on to provide what it describes as ultrasonic Doppler probe that can be introduced intracranially and manipulated to the desired configuration for traversing the natural spaces, i.e., the ventricles and cisterns, of the brain to measure blood flow at a particular site upon a cerebral vessel to help determine whether an aneurysm has been successfully treated. The probe includes means 22 said to be used in fixing the orientation of the operative surface with respect to at least one longitudinal axis of the sheath, or to the distal ends of the electrically conductive wires.
It can be seen, therefore, that while Doppler probes are helpful in blood flow monitoring, they suffer from several drawbacks. One drawback with implanted probes arises in the present inability to reliably and stably position the probe either within or about a vessel. A probe must be positioned securely about a blood vessel so that a transducer will be properly oriented to receive consistent signals from that blood vessel. Surgeons often report difficulties in positioning the probe because they must manually position the probe about the vessel with their hands or with forceps. Positioning the probe is also problematic because of the restricted space in the body in which the surgeon has to work. These problems of positioning also increase the risk that the probe would be accidentally detached from the blood vessel and lost in the body. Accordingly, there remains a need for a device and method that will enable a surgeon to position a probe about a blood vessel with more consistency and greater ease.